Self-Pressure Silicon–Carbon Anodes for Low-External-Pressure Solid-State Li-Ion Batteries

Abstract

Although a high stack pressure (≥50 MPa) enhances solid–solid contacts in solid-state batteries (SSBs), it poses impracticality for commercialization. This work proposes a self-pressure silicon (Si)-carbon composite anode that enables stable operation under reduced external pressure (≤2 MPa). The self-pressure anode features a prestress structure that can effectively alleviate the internal and external stress simultaneously, which is fabricated with ionic-conductive poly(ethylene oxide) (PEO)/lithium salt-coated carbon nanotubes (CNTs) being compressed by shrinking graphene hydrogel. The capillary-driven hydrogel shrinkage generates internal pressure, compensating for the volumetric expansion (up to 300%) of Si. This creates dynamic solid–solid interfaces between compressed CNTs/PEO and expanding Si, ensuring both mechanical stability and ion/electron transport. The SSBs with this self-pressure anode have a long cycle life of 700 cycles and a high capacity retention of 79.2% in an organic/inorganic composite electrolyte without external pressure (0 MPa). The half-cell using a sulfide solid-state electrolyte reached 700 cycles and was able to achieve a stable cycle life at the lowest 2 MPa stack pressure. This design resolves interfacial challenges by prestress in SSBs.